SPIM DEBUGGER QUICK GUIDE

SPIM is a MIPS32 simulator. If you run your code inside SPIM you can
use SPIM as a debugger. Unfortunatly, you cannot pass anything in command line
arguments. Thus, you will need to hard-code any command line args before using
SPIM as a debugger. 

STEP 1.
You first need to create labels that you may want to use as breakpoints. At
the very top of your text section use the assembler directive .globl for
any label you wish to use as a breakpoint:

    .text
    .globl main
    .globl b1
    .globl b2
    .globl fill_loop

STEP 2.
Next put the breakpoints in your code as places you wish to take a close look
at. For example:

fill_loop:        
   move $t2, $t1  
   mult $t2, $t2   
   mflo $t2       
   sw $t2, ($t0)      
   # set a breakpoint here so you can check the value in $t2 
   b1:

STEP 3. 
Execute Spim and run your code. Sample Session:

$ spim
(spim) re "test.s"
(spim) breakp b1 
(spim) run
Breakpoint encountered at 0x00400024
(spim) p $t2       # print value in register $t2
Reg 10 = 0x000000A2 
(spim) s           # step 1 instruction
(spim) s 5         # step the program for 5 instructions
(spim) print_sym   # print all global symbols
(spim) help        # display all instructions
(spim) cont        # continue executing until next break point
(spim) list        # list all breakpoints
(spim) exit


From help:
exit  -- Exit the simulator
quit  -- Exit the simulator
read "FILE" -- Read FILE containing assembly code into memory
load "FILE" -- Same as read
run <ADDR> -- Start the program at (optional) ADDRESS
step <N> -- Step the program for N instructions (default 1)
continue -- Continue program execution without stepping
print $N -- Print register N
print $fN -- Print floating point register N
print ADDR -- Print contents of memory at ADDRESS
print_symbols -- Print all global symbols
print_all_regs -- Print all MIPS registers
print_all_regs hex -- Print all MIPS registers in hex
reinitialize -- Clear the memory and registers
breakpoint <ADDR> -- Set a breakpoint at address ADDR
delete <ADDR> -- Delete breakpoint at address ADDR
list -- List all breakpoints
dump [ "FILE" ] -- Dump binary code to spim.dump or FILE in network byte order
dumpnative ["FILE"]-- Dump binary code to spim.dump or FILE in host byte order

Notes on SPIM:
The error "Attempt to execute non-instruction at 0x(address)00" where
address is the next address after your program ends means you did not
execute the syscall to exit

The first executable instruction must be preceded with label "__start:" or
by the directive if you want it to be something other than main: 

   .globl __start 
   main:

When you step through a program in SPIM the first instructions are setup
instructions that are not part of your program.